1. Field of the Invention
The present invention relates to an image capture apparatus and a control method therefor, and in particular to an image capture apparatus with an optical anti-shake mechanism and a control method therefor.
2. Description of the Related Art
Conventionally, a so-called image stabilization function is known that corrects (alleviates) blurring of a captured image (image shake) caused by a movement of an image capture apparatus, and representative methods for realizing the image stabilization function include optical image stabilization and electronic image stabilization (Japanese Patent Laid-Open No. 2011-145604). The optical image stabilization is a method for reducing a movement of an image of a subject by moving optical elements such as a shift lens and an image sensor based on a detected amount of shake of an image capture apparatus. On the other hand, the electronic image stabilization is a method for reducing a movement of an image of a subject by setting an effective pixel region smaller than a capturable range and shifting the position of the effective pixel region based on a detected amount of shake of an image capture apparatus.
Blurring of a captured image (image shake) caused by a movement of an image capture apparatus includes not only translational (translational direction) components that can be corrected using an image stabilization method described in Japanese Patent Laid-Open No. 2011-145604, but also rotational direction components, such as yaw, pitch, and roll components, attributed to a rotation of the image capture apparatus (rotational shake). Meanwhile, Japanese Patent Laid-Open No. 2008-5084 discloses a technique to correct an image shake related to rotational direction components of the shake by detecting motion vectors from a captured image and applying geometric deformation processing to the captured image in accordance with the motion vectors.
An image correction technique using the geometric deformation processing can be utilized not only for correction of rotational direction components of the shake, but also for correction of optical aberration, correction of a rolling shutter distortion unique to a CMOS image sensor, correction of a distortion that occurs in a case where an image of a subject is captured from below (projection distortion), etc. In view of this, it is thought that more advanced anti-shake effects can be achieved by applying the geometric deformation processing to an image for which optical hand movement correction has been performed (optical anti-shake image).
However, a method for detecting and estimating an image distortion using motion vectors at the time of application of the geometric deformation processing lowers the accuracy depending on scenes, increases an amount of computation necessary for high-accuracy estimation, and makes the estimation itself difficult. For example, in the case of a low-contrast image, such as an image captured indoors, it is more likely that motion vectors fail to be detected and erroneous motion vectors are detected. Therefore, for example, if a rolling shutter distortion is corrected in accordance with a moving subject, there is a possibility of the occurrence of harmful effects, e.g., a distortion of a portion that is supposed to be still, and a continuous image shake after the correction.
Furthermore, if a rolling shutter distortion in the roll direction is estimated from motion vectors simultaneously with the shake, there will be more estimation variables, leading to an explosive increase in an amount of computation and destabilization of solution estimation. Furthermore, it is basically not easy to estimate a rolling shutter distortion from motion vectors with high accuracy. Moreover, the difficulty will further increase if correction parameters for a radial distortion and optical aberration such as transverse chromatic aberration are simultaneously estimated from motion vectors.